Method and apparatus for spraying agglomerating powders

ABSTRACT

An apparatus for pneumatically spraying dry powders through a delivery tube from a fluidized powder reservoir having a bed powder chamber housing within the reservoir to provide an elongated chamber communicating with the delivery tube. The housing has an opening through a wall thereof, a sliding gate valve to selectively close the opening, and a wiping device on the valve to wipe the edges of the opening whenever the valve is activated. Means are provided for blowing a low-velocity purging gas through the powder chamber and delivery tube when the opening through the wall of the powder chamber is closed, and a highvelocity spraying gas when the opening is open to admit fluidized powders.

United States Patent Mester et al.

[ Aug. 12, 1975 METHOD AND APPARATUS FOR SPRAYING AGGLOMERATING POWDERS Assignee: United States Steel Corporation,

Pittsburgh, Pa.

Filed: Sept. 23, 1974 Appl. No.: 508,495

[52] U.S. Cl. 239/123; 34/85; 118/302; 222/342; 239/143; 302/52; 302/58 [51] Int. Cl B05b 15/02 [58] Field of Search 239/104, 106, 114-116, 239/123, 143, 346, 373, 398, 407; 259/4, D16. 17; 15/246; 302/52, 56, 58; 222/193, 342; 34/57 R, 57 A, 85; 118/302, 308-312; 51/8 R, 1 1

[56] References Cited UNITED STATES PATENTS 2,781,154 2/1957 Meredith 222/193 3,284,608 11/1966 McDonald 239 115 ux 3,345,111 10/1967 Bies et al. 302/52 X 3,430,643 3/1969 Heiland 239/1 14 X FOREIGN PATENTS OR APPLICATIONS 686,283 5/1964 Canada 118/308 Primary ExaminerM. Henson Wood, Jr. Assistant ExaminerAndres Kashnikow Attorney, Agent, or FirmForest C. Sexton [57 ABSTRACT An apparatus for pneumatically spraying dry powders through a delivery tube from a fluidized powder reservoir having a bed powder chamber housing within the reservoir to provide an elongated chamber cornmuni- 9 Claims, 5- Drawing Figures PATENTED AUG] 2 I975 SHEET Kn Y M SHEET PATENTEU Ausi 21975 QMQ m QR

SHEET x $103. 0Q Y METHOD AND APPARATUS FOR SPRAYING AGGLOMERATING POWDERS BACKGROUND OF THE INVENTION During various steel finishing processes wherein a steel is shaped or formed while the steel is in a heated condition, there are associated operations wherein it is desirable to mark the hot steel, for example, identification markings, locating defects, etc. Since the steel is hot, ordinary marking materials such as paint cannot be used as these would quickly burn off. Hence, the practice has been to apply dry powder pigments or metallic powders onto the hot steel surface, preferably by pneumatically spraying such powders.

Although there is a selection of commercially available equipment for spraying dry powders, such prior art equipment has not been suitable for spraying the types of powders used to mark hot steel. That is to say, the powders most commonly preferred for marking hot steel, e.g. titanium dioxide, zinc oxide, etc., tend to agglomerate when pneumatically pumped, and thus frequently plug and clog the powder spraying equipment. Even the use of tetrafluoroethylene linings, extra-dry air, and free-flowing additives such as silicon dioxide do not completely obviate the clogging problem.

SUMMARY OF THE INVENTION This invention is predicated upon our development of an apparatus for spraying dry powders which tend to agglomerate and is characterized by non-clogging and self-cleaning features.

Accordingly, an object of this invention is to provide an apparatus for spraying dry powders.

Another object of this invention is to provide an apparatus for spraying dry powders which is characterized by non-clogging and self-cleaning features and hence is ideally suited for spraying dry powders which tend to agglomerate and clog conventional spraying devices.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevation view in partial section showing an apparatus for spraying dry powder in accordance with one embodiment of this invention.

FIG. 2 is a plan view of the apparatus shown in FIG. 1.

FIG. 3 is an elevation view of a powder chamber incorporating another embodiment of this invention.

FIG. 4 is a plan view of the powder chamber shown in FIG. 3.

FIG. 5 is a schematic diagram of the pneumatic control circuit for operating the apparatus shown in the other figures.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to FIGS. 1 and 2, one embodiment of this invention comprises a fluidized bed powder reservoir 10, a powder chamber 12 and an air cylinder 14. The fluidized bed powder reservoir is of the type well known in the art and is commercially available (e.g. Ransburg Electro-Coating Corporation, Model No. 13893). The powder chamber 12 is basically a tubular type structure having a horizontal opening therethrough, and is attached to an inside wall of reservoir 10. As shown, powder chamber 12 is held against face plate 16 by nozzle adapter 18 and collar 20, and face LII plate 16 is held against the wall of reservoir 10 by nuts and bolts 22. Nozzle adapter 18 may be locked in position by roll pin 24. Delivery tube 25, through which the powder is sprayed, is attached to the outside end of nozzle adapter 18.

The powder chamber 12 has an elongated opening 26 through the upper side thereof to permit passage of fluidized powders from reservoir 10 in through the elongated opening through powder chamber 12. Sliding gate 28, a sleeve-like member closely encircling powder chamber 12, is provided to selectively expose and cover opening 26, thereby opening and closing powder chamber 12 to selectively admit fluidized powder thereinto. A wiper 30, consisting of a bolt or other such object, is attached to sliding gate 28 such that-.a lower extension thereof extends downward through opening 26 so that the edges of opening 26 are wiped clear of most powder adhering thereto whenever sliding gate 28 is activated to either the open or closed position. If necessary, an elongated plunger rod 32 is attached to the lower end of wiper 30 and extends horizontally to the opening in nozzle adapter 18 to loosen any agglomerated powder in the nozzle adapter 18 when sliding gate 28 is activated to the open position.

Sliding gate 28 is activated to the open and closed position by reciprocating air cylinder 14 attached to an outside wall of reservoir 10, opposite powder chamber 12, by bracket 38 and nuts and bolts, 40. Roll pin 42 anchors one end of air cylinder 14 to bracket 38 while stroke rod 44, extending from the other end is threaded into clevis 46, and there locked with locknut 48. Push rod 50 is attached to clevis 46 by pin 52 and extends through the wall of reservoir 10, with the inside end thereof secured to sliding gate 12, by screws 54 (FIG. 2). Grommet 56 seals the opening in reservoir 10 through which push rod 50 passes. Spring 58 and washers 60 hold grommet 56 firmly against this opening.

U-tube 62 is provided inside reservoir 10 to admit compressed air or gas to the inside end of powder chamber 12. One end of U-tube 62 is attached to face plate 16 by bulkhead connector 64, while the other end is connected to powder chamber 12 by connector 66.

In operation, gate valve 28 is activated to the closed position, and the powders to be sprayed through delivery tube 25 are placed into reservoir 10 and fluidized in a conventional manner, i.e., by air passing through a porous membrane. Thereafter, purging air or other gas is admitted at low velocity to U-tube 62 at connector 64. This low-velocity purging air flows through U- tube 62, powder chamber 12 and out of the apparatus through delivery tube 25. The apparatus is thus activated and ready to spray powder on demand. To spray powder, the velocity of the air admitted at U-tube 62 is increased as gate valve 28 is opened by air cylinder 14 to admit fluidized powder to powder chamber 12. Thus admitted, the powder is pneumatically ejected through nozzle adapter 18 and delivery pipe 25. When it is desired that powder spraying be discontinued, air cylinder 14 is activated to close gate valve 28 as the air admitted to the powder chamber 12 is reduced back to a low-velocity purging blow. Each time gate valve 28 is opened or closed, wiper 30 wipes the edges of opening 26 to remove any agglomerated powder which may have formed thereon. In addition, the low-velocity purging blow maintained through powder chamber 12, nozzle adapter 18 and delivery tube 25 will keep this passageway clear of accumulated powders.

FIGS. 3 and 4 illustrate a different embodiment of this invention wherein a modified powder chamber and gate valve are provided. With reference to FIGS. 3 and 4, this embodiment comprises a powder chamber 112 having rectangular openings 126 in the upper and lower surfaces thereof. A gate valve 128 to close these openings is provided by inserting a tight fitting slidable sleeve within powder chamber 112. A wiper 130 to wipe the edges of opening 126 is provided by a pair of rectangular flanges on the forward edge of the gate valve 128 which extend through opening 126. In this embodiment, U-tube 162 must be flexible as it is connected to pipe T-coupling 166 which is in turn secured between gate valve 128 and push rod 150. To open gate valve 128, an air cylinder (not shown) is activated to pull push rod 150 to the left. This pulls T-coupling 166 and gate valve 128 to the left as well as wipers 130 thus exposing the inside of powder chamber 112 to the fluidized powders. In all other respects, this embodiment is substantially the same as the first described embodiment.

Reference to FIG. 5 will illustrate the pneumatic control circuit used to operate the first described embodiment. With reference to FIG. 5, compressedair is admitted through valve 70, air and oil filter 72, and filter/dryer 74. From filter/dryer 74, the compressed air follows three lines, one line 76 to activate the fluidized powder reservoir 10, where valve 78 admits air to needle valve 80. Low velocity air flows continuously through needle valve 82 and line 84 to provide the low velocity purging blow through powder chamber 12 and delivery tube 25. A four-way solenoid air valve 86, operated by switch 88 is provided to activate the powder spraying mechanism. When powder is not being sprayed, switch 88 is open and no air is being admitted through valve 86. At this point, only the low velocity purging air is being blown through powder chamber 12, and gate valve 28 thereon is in the closed position so that fluidized powder is not admitted thereto. To commence blowing powder, switch 88 is closed to open valve 86 allowing high velocity air to flow through adjustable air regulator and filter 90 via line 92. From regulator and filter 90, line 93 delivers the high-velocity air to air cylinder 14 to thereby open gate valve 28 and admitfluidized powder to chamber 14, while line 94 delivers high-velocity air to U-tube 62 and accordingly powder chamber 12 and thus blows the powder therein through delivery tube 25. When it is desired to stop spraying powder, switch 88 is reopened which directs the high-velocity air through line 96, and adjustable air regulator and filter 98 to the other end of air cylinder 14 thereby reversing its position to close gate valve 28, while at the same time, the air admitted through line 92 is discontinued. With gate valve 28 closed, only the low-velocity purging air is admitted through powder chamber 14 and delivery tube 25.

In development work testing the above-described apparatus, .no critical limits were noted with respect to air pressure and flow rates. In order to present a clearer understanding of its operation however, it is noted that the apparatus was operated quite successfully with source air pressures of to 100 psi, with purging air blow rates of 35 to 45 CFM, and spraying air blow rates of 80 to CFM. In these tests the delivery tube 25 had an inside diameter of %-inch, with a calculated outlet pressure of about 40 psi.

We claim:

1. An apparatus for pneumatically spraying dry powders through a delivery tube comprising a fluidized bed powder reservoir, a powder chamber housing attached within said reservoir having an elongated chamber therein communicating with said delivery tube and an opening in a wall thereof communicating with the interior of said reservoir through which fluidized powders may be admitted, a valve means for closing said opening, wiper means attached to said valve means for wiping the edges of said opening whenever said valve means is activated to thereby keep said opening clear, means for blowing gas through said powder chamber housing and delivery tube with a low-velocity purging blow when said valve means is in a closed position and with a high-velocity powder spraying blow when said valve means is in the open position.

2. An apparatus according to claim 1 in which said powder chamber housing is attached to an inside wall of said reservoir and said delivery tube is attached on the adjacent outside wall so that the powder chamber and delivery tube communicate through the reservoir wall.

3. An apparatus according to claim 1 in which said powder chamber housing is of a substantially cylindrical configuration. 1

4. An apparatus according to claim 1 in which said valve means comprising a slidable gate which is operated by an air cylinder.

5. An apparatus according to claim 4 in which said air cylinder is attached to an outside wall of said reservoir.

6. An apparatus according to claim 4 in which said slidable gate comprises a sleeve-shaped member encircling said powder chamber housing.

7. An apparatus according to claim 4 in which said slidable gate comprises a sleeve-shaped member slidably inserted within said powder chamber housing.

8. An apparatus according to claim 4 in which said wiper means comprises a body attached to said slidable gate extending through the opening in the wall of said powder chamber housing.

9. An apparatus according to claim 4 in which said slidable gate has an elongated plunger rod attached thereto which extends through at leasta portion of the powder chamber and to the delivery pipe such that when the slidable gate is activated to the open position, said plunger rod is advanced into the delivery tube to loosen any agglomerated powder therein. 

1. An apparatus for pneumatically spraying dry powders through a delivery tube comprising a fluidized bed powder reservoir, a powder chamber housing attached within said reservoir having an elongated chamber therein communicating with said delivery tube and an opening in a wall thereof communicating with the interior of said reservoir through which fluidized powders may be admitted, a valve means for closing said opening, wiper means attached to said Valve means for wiping the edges of said opening whenever said valve means is activated to thereby keep said opening clear, means for blowing gas through said powder chamber housing and delivery tube with a low-velocity purging blow when said valve means is in a closed position and with a high-velocity powder spraying blow when said valve means is in the open position.
 2. An apparatus according to claim 1 in which said powder chamber housing is attached to an inside wall of said reservoir and said delivery tube is attached on the adjacent outside wall so that the powder chamber and delivery tube communicate through the reservoir wall.
 3. An apparatus according to claim 1 in which said powder chamber housing is of a substantially cylindrical configuration.
 4. An apparatus according to claim 1 in which said valve means comprising a slidable gate which is operated by an air cylinder.
 5. An apparatus according to claim 4 in which said air cylinder is attached to an outside wall of said reservoir.
 6. An apparatus according to claim 4 in which said slidable gate comprises a sleeve-shaped member encircling said powder chamber housing.
 7. An apparatus according to claim 4 in which said slidable gate comprises a sleeve-shaped member slidably inserted within said powder chamber housing.
 8. An apparatus according to claim 4 in which said wiper means comprises a body attached to said slidable gate extending through the opening in the wall of said powder chamber housing.
 9. An apparatus according to claim 4 in which said slidable gate has an elongated plunger rod attached thereto which extends through at least a portion of the powder chamber and to the delivery pipe such that when the slidable gate is activated to the open position, said plunger rod is advanced into the delivery tube to loosen any agglomerated powder therein. 